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Explain plan in Oracle

I want to show the usage of an explain plan in Oracle. This will be shown in Oracle 12c. I will create a table and a sql statement. This sql statement will be analysed in a so-called explained plan that shows how Oracle will process the query. To do so, I first created a big table “Groot” in Oracle. Upon that I created an index “GrootIndex” with create index grootIndex on groot(n).
The explain plan is created with (select * from C##HR.GROOT where n=600000; being the sql statement) :